Ballast construction



C 27, 19 J. c. YAEGER 2,910,623

' BALLAST CONSTRUCTION Filed June l5, 1956 n k," l JH N l 1 l l l l 8 ll l l I IQ. z I 3 f| l 6 l "I l g l 5 j C 9 i A 1 l lo l l JNVENTOR.JOSEPH Cl` Yat-:GER

Avvaanev United States Patent BALLAST CONSTRUCTION Joseph C..Yaeger,Milwaukee, Wis., .assignor. to McGraw- Edison Company, a corporation. ofDelawaren Application June 115, 1956t,Serial'-No. 591,711-l 3 Claims.(Cl.` 3159-241) This invention relates to` a. constant wattage ballastconstruction whichis particularly usefulinmercury vapor lighting systemswhere av separate ballastisrprovided; for each lamp.

In mercury vapor lighting systems where` the mercury vapor lamps areplaced inshunt, `it isacustomary practice to provide each lamp` with anindividual constant wattage ballast. These ballasts areunitswhichcomprise in effect a transformer and condensers associatedtherewith, in. which the. transformers are` usually so. constructed thata magnetic shuntV or magnetic leak. isprovided.V

It has been found that when` the.` lamp, current crest factor,. which isthe` ratio of the peak current to,V the Rit/LS.,y is high that thetotal. output of.y lightl for thelife ofthe lamp is lower than where thecrest factor is` lower. While the theory isnot entirely clear it` isbelieved that this is due to the factthat the low. electron affinitymaterial with which the` one or more electrodes` ofithe mer.- cury vaporlamp are provided seems to boil out or to be driven oiffor thev highfcurrent` peaksW-hereithere. is `a highcrest factor. This materialcollects or condenseslon the inner Walls of thev quartz or hardflglasstube of the mercury vapor lamp, and lowers the lumen. output of the lampafter a relatively short periodA of use4 so that during the entire lifeperiod` of the lamp itsytotall light output is less than where thecrest` factor` isi lower. The lower crest factor occurs whenY the peak.or crestcurrent is relatively low whereas, on `the other hand, the peakor crest current for a2 high crest factor is, relatively high.Consequently, for a low crest factor there is less chance of the boilingoff or driving off of the" low electron ainity: material with thedeleterious effects hereinabove noted.

In ballasts of the above type, it is the usual practice to provide tworesonant circuits assoeiatedwith theLsecondary` or output portion of thetransformer of ther constant wattage ballast. It is the customarypractice to so arrange the circuits that what may be called the firstresonant circuit, resonates at the third harmonic and is employed tosecure a high striking or starting Voltage for the mercury vapor lamp.In the customary practice, what may be called the second or operatingcircuit is so arranged that it resonates at the fundamental frequency.

It has been found through extensive experimentation that in the usualforms of ballasts hereinabove discussed, the third harmonic is stillpresent in an undesirably high value during the normal operation of thelamp and con,

sequently the lamp current crest factor is high, thus limiting orlowering the entire output during the total life period of the lamp. i

This invention is designed to provide a constant Wattage ballast whichhas a low value for the third harmonic current during the operatingperiod of the lamp, that is to say, while the lamp is hot and isoperating in its normal capacity. As shown hereinabove, this reduces theamount of low electron affinity material that is driven off from anelectrode of the lamp since the peak value ice 2 of the:alternatingcurrent during operating conditions is lower due to thereduction of the third harmonic.

It has been found further that where the crest factor isihigh,thatthe'warmmp-period of theV lamp is-` increased overaA that requiredwhere the crestv factor` is lower. In certain. instances thelamp nevenf-ully warms up andfconsequently fails `to function properly, Where theorest=factor1` is high. It is, therefore, a further object to provide.`a ballast which is` soconstructed that the warm-ups period of the..vmercury vapor lamp `is reduced;

Aspecific object of` this invention is tofprovide aibaldlasticonstruction in.y which one of=` the elements of theres.d onantIcircuit'. which resonates:1 atY the third harmonicv is; in effectAshortediout or. partially shortediout duringi the.` op.-eratingperiodofthelamp, so thatY the value` of. thethird.` harmoniccurrent, when the lamp is. in.` operation,.is.greatly reduced while` at'the` sametime the outputacircuit is arrangedtto resonate at` 60 cycles.`

Anembodimentf of the invention is shown in the accompanying drawings inwhich:

liigure.I l1 isia diagrammatic` view of the` constant` wattage4 ballast.

Figure-2 is afragmentanyview ofa portion of:` theibal-iA last showingprimarily.` themagnetic core and windings;

Itis: customary to: constructthe ballast as a unitary structure. with-`all of:V the` component parts carried` in a housing or casing. Thisdiagrammatically shown` in Figure lby the, dotted line,V indicated bythe reference character 1. y

The. transformer consists-1 of the main core 2= of larni` nated materialprovided. with. magnetic shunts= 3. AS1` a matter of fact, thetransformer is not made` of an unbroken sheet for each lamination asindicated in Figure 2, but is made of the usual strips orpunchings.which,r are built up intoi the; final' forinshown. in Figure2. The magnetic shunts are` diagrammatically shown in Figure l. Theshunts maybe formed as shown in-Figure 2` and-indicated at` 3 bysuitably stamping out' the` core 2.. The; primary is` shownA at 4- and`thesecondary at Si. TheV primar-yf may have. taps if desired, onmay beformed 'as-shown in Figr ure` l` of: two windings` which may be`connectedV either in shunt. or in parallel, for la120-l=30 volts1 or220-260 volts. The secondary supplies a.- single mercury vapor lamp`indicated, by the` reference character 6.` Inf` the system. oft mercuryvapor lighting for which this.` ballast is made each lamp. is. provided`with` its` own individual ballast'.`

A relatively large; capacitor indicated bythe reference character, 7 isplaced in series with the secondary 5 and is shunted: by, ahighresistance leak. of theforder of several, hundredthousand ohms.. Acapacitor 9 of relatively low capacitance, as compared with thecapacitor 7, is connected directly across the output leads from thesecondary '5. lIt is to be noted particularly that the capacitor 7 isconnected on the outer side or delivery side between the lamp 6 and therest of the secondary circuit. This is a very important feature of theinvention. It is connected in such a manner as shown in Figure l thatthe lamp 6 directly bridges the capacitor 9.

When the lamp is not in operation, that is to say, when the lamp iscold, the capacitor 9 is effective and forms a portion of a resonantcircuit including the capacitor 9, the capacitor 7, and the secondary 5.This circuit resonates for the third harmonic. However, when the lamp 6is in operation, it provides a shorting or bridging circuit directlyacross the capacitor 9 thereby greatly lessening the effect of thecapacitor 9 or else entirely suppressing the action of the capacitor 9so that the resonant circuit hereinabove mentioned for the thirdharmonic no longer exists, or if it operates at all in resonance, itseffect is tremendously reduced.

On the other hand, when the lamp has struck and is operating, it forms aportion of a resonant circuit including the lamp 6, the capacitor 7 andthe secondary 5. This circuit resonates at the fundamental frequency.During the normal operation of the lamp the third harmonic ispractically, if not entirely, suppressed as explained hereinabove.

' The input and output terminals of the constant wattage ballast areindicated by the reference characters 11, I11 and 10, respectively. Itis to be understood that the magnetic shunts 3 operate in the usualmanner to limit the current by providing a leakage path for the magneticux.

It will be readily seen that the crest factor is greatly reduced duringoperating conditions of the lamp since the third harmonic is materiallyreduced if not completely suppressed. In other words, the lamp 6 tendsto short out the capacitor 9 and consequently to suppress the'thirdharmonic which causes thes high peaks in the alternating current wave.This suppression of the third harmonic results in the low crest factor.vI.It is essential that the capacitor 9 be connected at a point beyondthe capacitor 7. That is to say on the side of the capacitor 7 oppositethe secondary 5, as explained hereinabove.

It will be seen that a relatively simple construction is provided bythis invention in which the ballast produces the minimum of the thirdharmonic, and consequently greatly reduces the value of the crestfactor.

From actual tests it has been found that the warm-up period of the lampis materially reduced by reducing the crest factor as hereinabove setforth. 1 Although this invention has been described in considerabledetail, it is to be understood that such description is intended asillustrative rather than limiting, as the invention may be variouslyembodied and is to be interpreted as claimed.

I claim:

1. A mercury vapor alternating current lighting system for striking andoperating mercury vapor lamps comprising a ballast having input andoutput terminals, a mercury vapor lamp connected across the outputterminals, said ballast comprising a transformer having a primaryconnected to the input terminals and having a secondary, a relativelylarge capacitor connected in series between an output terminal and oneside of said secondary, the other side of said secondary being connectedto the other output terminal, a relatively small capacitor connectedacross the output terminals between theV output terminals and the firstmentioned capacitor and being directly bridged by said mercury vaporlamp, whereby when said mercury vapor lamp is lighted it forms a shortcircuit directly bridging said second mentioned capacitor, the lamp, therelatively large capacitor, and the secondary forming the major part ofa circuit resonating at the fundamental frequency, and the relativelysmall capacil tor, the relatively large capacitor, and the secondaryforming a circuit resonating at an odd harmonic frequencyi 2. A mercuryvapor alternating current lighting system for striking and operatingmercury vapor lamps comprising a ballast having input and outputterminals, a mercury vapor lamp connected across the output terminals,said ballast comprising a transformer having a primary connected to Itheinput terminals and having a secondary, said transformer having magneticshunting means provided with an air gap and located between said primaryand said secondary, relatively large capacitor means connected in seriesbetween an output terminal and one side of said secondary, 'the otherside of said secondary being connected to the other output terminal, arelatively small capacitor connected across the output terminals betweenthe output terminals and said capacitor means and being directly bridgedby said mercury vapor lamp, whereby when said mercury vapor lamp islighted it forms a short circuit directly bridging said relatively smallcapacitor, the lamp, the relatively large capacitor means, and thesecondary forming the major part of a circuit resonating at thefundamental frequency, and the relatively small capacitor, therelatively large capacitor means, and the secondary forming a circuitresonating at an odd harmonic frequency.

3. A mercury vapor alternating current lighting system for striking andoperating mercury vapor lamps comprising a ballast having input andoutput terminals, a mercury lvapor lamp connected across the outputterminals, said ballast comprising a transformer having a primaryconnected to the input terminals and having a secondary, a relativelylarge capacitor means connected in series between the output terminalsand said secondary, a relatively small capacitor connected across theoutput terminals between the output terminals and said capacitor meansand being directly bridged by said mercury vapor lamp, whereby when saidmercury vapor lamp is lighted it forms a short circuit directly bridgingsaid relatively small capacitor, the lamp, the relatively largecapacitor means, and the secondary forming the major part of a circuitresonating at the fundamental frequency, and the relatively smallcapacitor, the relatively large capacitor means, and the secondaryforming a circuit resonating at an odd harmonic frequency.

References Cited in the file of this patent UNITED STATES PATENTS2,355,360 Boucher et al Aug. 8, 1944 2,429,162 Keiser Oct. 14, 19472,439,976 Keiser et al Apr. 20, 1948 2,496,981 Boucher Feb. 7, 19502,858,479 Sola Oct. 28, 1958

